Gut microbiota may influence the effectiveness of the drugs we take and even medical treatments for infections—such as those caused by HIV—or cancer. This was one of the main messages presented at the latest edition of BDebate, an international experts’ conference promoted by Biocat – the organization that coordinates and promotes the healthcare and life sciences sector in Catalonia- and the financial institution ‘la Caixa’ social project fund, held in Barcelona to discuss the latest research in the human microbiome.

Núria Malats is a researcher at the Spanish National Cancer Research Centre (CNIO) and a member of the conference’s science committee. She specialises in pancreatic cancer, which involves one of the most aggressive tumours in the gastrointestinal tract, and is interested in identifying how bacteria in the oral cavity might increase the risk of pancreatic cancer.

Recent studies have shown that there may be a link between the microbiota and the effectiveness of some drugs and even some treatments, such as the antimicrobial gel used to prevent the transmission of HIV. In the case of cancer, do researchers believe the microorganisms found in the gut could have an influence on chemotherapy?

Even though we are in the early stages, there is some evidence for this. For instance, we are noticing that a patient’s immunological state can be modulated by altering the microbiota, which therefore has an effect on cancer treatment. This is a very promising field, because some cancer therapies can be modulated by modifying the microbiota, but these options are still at a preliminary stage.

Gut microbiota has been associated not only with treatment but also with the development of the cancer itself.

That’s right, and there are several examples. Perhaps the most paradigmatic is the case of colon cancer, where the results are pretty reliable and conclusive. It happens in other cancers as well. For instance, I work on the pancreas, where there is also a relationship between microbiota and tumour. Perhaps in this case the association is not so much with the gut microbiota—there probably is a relationship but it has not been studied as much—rather, the early results relate to the oral microbiota.

In this regard, there are a few studies that stand out: the first was carried out with a large European cohort, in which serum antibodies that fight oral germs, such as Porphyromonas gingivalis, were identified and which are associated with an increased risk of pancreatic cancer. There is also another study with American cohorts that has also corroborated the presence of this germ in the oral cavity and it has been associated with an increased risk of pancreatic cancer.

Are these just correlations or do we know which mechanisms lie behind them, which lead to certain bacteria increasing the risk of pancreatic cancer?

They are correlations. We are still in the early stages. Nothing has been proven. The idea is that we swallow the germ, it goes through the digestive tract and reaches the colon, possibly reaching the pancreas this way. The germ leads to chronic infection—a parainflammation—and this parainflammation would be the factor promoting the pancreatic cancer. However, we do not yet know what the mechanisms behind this are. With colon cancer, however, more mechanistic studies have been carried out looking specifically at microbes and how they affect a tumour’s development.

When did we first suspect that cancer could be related to gut microbiota?

The early studies associating cancer with gut microbiota are relatively recent, around 5 or 10 years old. That is when the microbiota started to be decrypted in terms of the gut and was associated with different illnesses. Inflammatory bowel disease is the most obvious, followed by cancer.

We know cancers are complex multi-factor diseases, so any suggestion that can provide information about the etiological scenario—the disease’s origin—and the factors involved and how they interact is important. Those of us working in the field of cancer quickly started to become interested in exploring the relationship with the microbiota.

In the case of pancreatic cancer, the bacteria that began to be associated with the disease are also associated with other risk factors for pancreatic cancer, such as diabetes mellitus, asthma and obesity.

Can we use our diet to promote a rich, varied and balanced microbiota and help with treating some illnesses?

This is a slightly controversial issue. On the one hand, you have those who defend the issue of diet and on the other, those who defend more specific treatments. In my opinion, it will probably be a combination of these two things. For example, I cannot imagine patients with pancreatic cancer, who are diagnosed at an advanced stage, trying to modulate chemotherapy with diet alone. To modify or boost the treatment of cancer patients, you probably need more specific strategies. On the other hand, in the field of prevention, a diet that includes prebiotics and probiotics may have a significant effect.

Cristina SáezCristina Saez is a freelance science journalist. She works for several media, for instance the Spanish newspaper La Vanguardia, where she coordinates the science section, Big Vang; as well as research centres and scientific societies. She has been awarded for her journalistic work, among others, with the Boehringer Ingelheim Award in Medical Journalism 2015. Follow Cristina on Twitter @saez_cristina

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Gut Microbiota for Health has been created by the Gut Microbiota and Health Section of the European Society for Neurogastroenterology & Motility (ESNM), member of United European Gastroenterology (UEG)